1. Field of the Invention
The present invention relates generally to freight loading and unloading crane systems. More particularly, present invention concerns a novel dual trolley, single boom crane system that effectively doubles the rate of container loading and unloading of conventional prior art single boom crane systems. The present invention also concerns a novel method for retrofitting conventional prior art single boom crane systems to convert them to dual trolley systems.
2. Discussion of the Prior Art
A typical prior art single boom, single trolley container crane of the character currently found at many shipping container harbor terminals throughout the world is illustrated and FIGS. 1 and 1A of the drawings. These crane systems use a single trolley running on a single, continuous boom. A major problem with such systems is that the ability to use only a single trolley in such systems drastically restricts the capacity of the system. For this reason a number of attempts have been made in the past to modify the typical prior art single boom, single trolley crane systems in a manner to increase the rate at which containers can be handled by such systems. Exemplary of such an attempt is the container crane system illustrated and described in U.S. Pat. No. 6,976,599 issued to Rivera, et al. This patent discloses a crane apparatus that involves the use of a single crane through which repeated cycles of two simultaneously functioning trolleys may be moved along fixed paths on a boom. Pursuant to the Rivera, et al., invention, each of the trolleys is also moved along one of two parallel-spaced straight rail paths on a platform that is laterally displaced in a direction perpendicular to a fixed path on the boom for either straight-through transit of the trolley or lateral transfer thereof between fixed-boom rail paths so as to accommodate transfer of each trolley between the boom paths and either one of two loading and unloading positions under a central crane structure. One of the trolleys may thereby be cyclically emptied or loaded from one end of the boom, while the other trolley is either loaded with a container or emptied at one of the two positions underlying the platform. While the Rivera, et al., apparatus does indeed increase the loading/unloading rate, probably by a factor of 1.5, the increased width of the apparatus would, however, permit fewer cranes to be simultaneously positioned over the ship.
A further prior art attempt to improve the rate of container loading and unloading of prior art single boom, single trolley crane systems is disclosed in U.S. Pat. No. 6,981,598 also issued to Rivera, et al. Pursuant to this latest Rivera, et al., disclosure, a single crane is provided through which repeated cycles of two simultaneously functioning trolleys may be moved along a fixed-boom rail path and one of two 90 degree related rail paths on a turn-table platform pivotally mounted for rotation about an axis at the intersection of such platform rail paths so as to accommodate transfer of each trolley between the fixed-boom rail path and either one of the two platform rail paths positioned in alignment therewith by angular displacement of the turn-table platform. One of the trolleys may thereby be cyclically emptied or loaded from one end of the boom while the other trolley is either loaded with a container or emptied at one of the two positions underlying the platform. As was the case with the earlier Rivera, et al., invention, the increased width of the apparatus would permit fewer cranes to be simultaneously positioned over the ship.
Still another approach to improving the rate of loading and unloading of containers from dockside ships is disclosed in U.S. Pat. No. 3,945,503 issued to Cooper. The Cooper patent discloses a crane structure supporting a gantry having a pair of trolley rails mounted thereon. At least one trolley is mounted on the rails and a load engaging means is suspended from the trolley by reeving depending from sheaves mounted on the trolley. Means are provided for moving the sheaves apart a selected distance to angulate the reeving with respect to the loader engaging means, and means are provided for moving the trolley along the gantry rails to transport a load between its pickup and deposition areas. The dampening of sway in the load is accomplished by a “fleet-through” reeving arrangement and without the necessity of mounting the hoisting drums on movable trolleys. Moreover, the present invention coordinates the movements of the trolleys with reference to a single load point and prevents rocking movement of the load about a horizontal axis.
Yet another approach to improving the rate of loading and unloading of containers from dockside ships is disclosed in U.S. Pat. No. 3,881,608 issued to Hupkes. The Hupkes patent concerns a bridge crane for loading and unloading containers or packing crates into and from a vessel that comprises a support structure including a horizontal girder on which one or more carriages are supported for movement each provided with hoisting and propelling devices. A positioning member is also supported for movement along the girder independently of the carriage and is provided with sighting means for determining the position of the positioning member along the girder with respect to the vessel therebelow. A device which may be in the form of an arm for actuating a switch is mounted on the positioning member to halt the carriage at a predetermined distance from the positioning member. In the case where two carriages are provided, one is superimposed on the other and is capable of traveling in a vertical plane therewith and therepast with a load suspended therefrom.
As will become apparent from the discussion that follows, the present invention uniquely provides a novel dual trolley, single boom crane system that effectively doubles the rate of container loading and unloading of that conventional prior art single boom crane systems.